The invention relates to the interpretation of formation tops from well log curves in order to identify the same features among the wells.
Collecting well log data from boreholes drilled in the earth provides information which may be analyzed for subsurface formation or formation top (e.g., a boundary between two formations) depth structure within oil or gas fields. The information derived indicates the type of rock in the subsurface. Nuclear, gamma ray, electromagnetic, sonic, magnetic, or other source instrumentation is lowered into the boreholes to generate source signals which probe the underground formations. The formations or formation tops modify or respond to the source signals, and sensors are disposed with the source instrumentation in the boreholes to monitor the resulting or modified response signals. The response signal characteristics, for example, its amplitude, vary with the different types of source signals and will also depend on the type of formation or formation top observed. These data are collected over time and are collectively called "well log curves" or "well logs." The well logs are typically recorded as a function of depth in the boreholes, one recorded curve (or trace) for each type of source.
Multiple boreholes may be used to collect data from multiple wells. Probing multiple wells makes it possible to track spatially the various formations or formation tops under test. Wells, for example, dozens of wells, may be bored at spacings miles apart for such analysis. Thousands of wells may be bored in more detailed studies, each of which are spaced from one-quarter to one-half mile apart. Boring to a typical depth of 10,000 feet allows multiple formations to be observed in the response traces. The geoscientist's challenge is to map the location of the subsurface formations from multiple numbers of well logs. This may involve trying to match features in traces recorded from one well log to similar features in traces from other (e.g., many other) well logs, a process called correlation. The interpretation of formation tops in oil or gas fields, however, may be a difficult and time consuming activity.